Connect new energy photovoltaic power generation to the grid



The quantity of traditional energy is limited and will bring damage to the environment. Energy saving and consumption reduction and large-scale development of clean new energy are the general trend of the world. The country has also formulated related policies, using solar photovoltaic power generation as one of them. But for the photovoltaic power generation and network and complete power distribution related knowledge, I think you are also very interested in understanding. Here are several aspects to learn together.

New energy power generation
New energy (NE), also known as unconventional energy. It refers to all forms of energy other than traditional energy sources. Classification of new energy: solar energy, wind energy, biomass energy, hydrogen energy, geothermal energy, ocean energy, small hydropower, chemical energy (such as ether-based fuel), nuclear energy, etc.

The characteristics of new energy: rich resources, generally with renewable characteristics, for human sustainable use; Low energy density requires large space for development and utilization; No carbon or carbon content is small, small impact on the environment; Wide distribution is conducive to small-scale dispersed utilization; Intermittent supply, high volatility, adverse to continuous supply; Except for hydropower, the development and utilization cost of renewable energy is higher than that of fossil energy.

Principle of photovoltaic power generation
Solar photovoltaic power generation relies on solar cell modules and makes use of the electronic properties of semiconductor materials. When sunlight irradiates on semiconductor PN junction, non-equilibrium electrons and holes in the barrier region or non-equilibrium electrons and holes outside the barrier region but diffused into the barrier region are generated due to strong built-in electrostatic field generated in the P-N junction barrier region. Under the action of the built-in electrostatic field, each moves in opposite directions, leaving the barrier region, resulting in an increase in the P-zone potential and a decrease in the N-zone potential, thus generating voltage and current in the outer circuit, converting light energy into electrical energy.

Classification of photovoltaic power generation systems
Solar photovoltaic power generation systems can be broadly divided into two categories:

One is grid-connected power generation system, which converts the received solar radiation energy into high-voltage direct current through high-frequency DC conversion through photovoltaic array, and then outputs sinusoidal AC current with the same frequency and phase as grid voltage to the public power grid after inverter inverter.

The other is the independent power generation system, that is, the circuit formed in its own closed circuit system, the first will receive the solar radiation energy directly converted into electricity supply load, and the excess energy through the charging controller, stored in the form of chemical energy in the battery.

Photovoltaic power generation grid-connected system distribution
The inverter output voltage or grid-connected voltage of the photovoltaic power generation system depends on the installed capacity of the photovoltaic power station. 8kW and below can be connected to 220V, 8-400kW can be connected to 380V, 400kW-6MW can be connected to 10kV,10MW can be connected to 30kV. The above grid-connected voltage may be the output voltage of the inverter, or the voltage boosted by the booster transformer after the output bus of multiple inverters. An example is shown in the figure below:

As shown in Figure 1, a small amount of photovoltaic power generation system is used for self-use and most of the rest is connected to the grid. The inverter is equipped with a series of protection functions such as island protection. When the mains is out of power, it automatically disconnects with the mains system. Within 5 minutes after the mains is restored, the inverter automatically connects to the grid to generate electricity. The voltage of 10kV distribution network metering point, metering meter for two-way metering. Note that no matter the low voltage or high voltage is connected to the grid, the measuring cabinet or measuring room must meet the requirements of the local power supply bureau.

Grid-connected island prevention measures
First understand the definition of island effect, etc. :

Isolated island effect: When the power grid loses voltage, the photovoltaic system still keeps supplying power to a certain part of the power grid.
Anti-islanding effect: When the grid into which the photovoltaic system is incorporated loses voltage, the photovoltaic system must be disconnected from the grid within a specified time limit to prevent the islanding effect.
Anti-island measures: can be used in two ways, the first, the use of photovoltaic special circuit breaker, which contains the anti-island required to collect a variety of electrical parameter signal input and on-off control; The second, the conventional circuit breaker can be remotely controlled at the same time, and then configure the anti-island device (similar to the comprehensive relay protection device), the acquisition of the input of the electrical parameters, as well as the control of the circuit breaker. Electrical parameters are usually voltage, frequency, etc., with reclosing, partial function on/off, delay on/off and so on. Can be selected and set according to the requirements of the local power supply bureau. Notice that all signal acquisition terminals are on the power grid side. It must be clear whether the power supply side of the photovoltaic circuit breaker refers to the power grid side or the photovoltaic module side.